The present invention relates generally to electrical connectors, and more specifically to liquid-tight conduit connectors which couple liquid-tight, flexible conduits to electrical fixtures, such as junction and outlet boxes.
Liquid-tight, flexible conduits are used to protect electric current-carrying wires. The wires are covered by one or more layers of insulation, such as rubber or plastic resin. The covered wires are then pulled through the longitudinal axial bore of the flexible conduit, thereby being protected.
Such a liquid-tight flexible conduit is employed in environments where the conduit is subject to multiple bends, heavy use, and chemical or liquid spray. There are numerous applications in household, commercial, and industrial building construction for this particular design of conduit hose. Traditionally, liquid-tight flexible conduit is made from helically wound and interlocked metal strips, and the resulting hose is covered by a plastic resin, such as polyvinyl chloride.
A less expensive conduit construction has been made from a unitary layer of plastic material, such as vinyl. Such material is flexible and liquid tight, and has gained great popularity. Typical connectors for this type of plastic conduit include those made by RACO, Thomas & Betts, Crouse & Hinds, and Appleton Electric Company. These connectors generally feature three or more parts, including a matable cap and body portions.
An annular region is defined by the interacting cap and body of the connector. The plastic conduit is actually held by the connector by initially screwing it to part of the connector body before sliding the cylindrically shaped cap over the conduit and screwing it into contact with the body.
A specialty user of plastic conduit is the machine tool industry, especially manufacturers of robotic equipment. Plastic hose might be used, for instance, to protect the wires electrically connecting the hand and body of a robot. Needless to say, such conduit must be flexible, since it constitutes the arm of the moving robot. Because of the particular applications of this type of conduit, it typically is made from multiple layers bonded together to comprise an integral conduit. For instance, there might be an inside layer made from polyvinyl chloride, neoprene, or polyethylene which provides a smooth inside wall with dielectric strength to meet the requirements of the wire passed through the bore of the conduit and coming into contact with this inside layer. The center layer, by contrast, might be made from fiberglass mesh to counteract the elongated resiliency of the other two layers and prevent stretching of the conduit under the stresses of robotic application, while still permitting flexibility. Finally, the outside layer might be made from vinyl to protect the conduit material from attack by, for instance, hydraulic oils, lubricants, chemical solvents, sunlight, ozone, and abrasion.
While connectors conventionally known in the art may be used in conjunction with this specialty category of conduit hose, there are disadvantages. The primary problem is that even the most meticulously manufactured multi-layer conduit generally will be eccentrically dimensioned. That is, part of the conduit wall will be broader at one point of the cross-section of the conduit than at another position. Such eccentrically dimensioned conduit poses problems for conventional connectors which have rigid cap and body walls defining a perfectly dimensioned annular cavity to accommodate the conduit wall. Because of the poor fit between the connector and conduit wall, a proper liquid-tight seal may not be realized. Moreover, the conduit is, in reality, clamped to these sorts of connectors by first screwing the inside wall surface of the conduit into contact with helical threads on a portion of the connector body element. The cap, itself, does not really hold the conduit. This makes assembly and disassembly a cumbersome process. The conduit can also rotate during use while "clamped" by the connector, and this can apply stress to the wires contained therein, which are connected to a stationary electrical source elsewhere. Furthermore, most of the conventional connectors known to those skilled in the art use a relatively high number of parts which, besides being cumbersome to assemble, are made from metal and require machining, thereby substantially increasing the cost of manufacture.